Apparatus for centrifugal separation with the use of an auxiliary liquid



April 28, 1953 J A ASPEGREN 2,636,670

APPARATUS PoR'cENTRIFuGAL SEPARATION WITH THE USE OF AN AUXILIARY LIQUIDFiled March 1, 1950 MIT Hg INVENTOR.

yo/m flxe/ flspegren BY mww kd m Patented Apr. 28,. 1953 APPARATUS FORCENTRIFUGAL. SEPARAv- TION WITH THE USE OF- AN AUXILIARY LIQUID.

I John A. Aspegren, Stockholm, Sweden; assignor to Akti'ebolagetSeparator, Stockholm, Sweden, 7

a corporation-ofi Sweden Application Marchl, 1950,. Serial. No. 147,094

In Sweden March 2-,. 1949 11: Claims. 1"? Thisiinvention relates tocentrifugalseparation with the use of an auxiliary liquid, to separateparticles of difierentispecific: gravity or size from one another: or toliberate solid particles from adhering liquid. More particularly; theinvention has reference to an improved method and apparatus for thispurpose.

In a copending application of Carl G. Eckers, Ser. No. 31,854, filedJune 9, 1948, now Patent No; 235951619; there'is disclosed a procedureutilizi'ng a separator bowl provided with a system oflchannels; outsidetheseparatingzone orcharnber; Through the channels, or part of them, an:auxiliary liquidflows in an inward direction, it bein possible tointroduce its in or outside the channels. At the same time, a suspensioncontaining solid particles, separated'f'rom the main liquid in theseparating" chamber; passes through the" channels in an outward"direction. In the channels, the main: liquid ofthe suspension ispartially replaced by auxiliary liquid. When the suspension containsparticles of different-specific gravity, or of thesame specific gravitybut substantiallydifierent size, it is also possible to obtain: asorting of the particles in the channels.

The specifically'heavier and the larger particles slide outward in spiteof the: inwardlydirected current, of: liquid: and can be dischargedthrough openings the bowl. wall. Thespecifically lighter and the smallerparticles follow the liquid current inwardly and mayleavethe bowlthroughoutlets::near to. its. rotation. axis.

The present invention. relat'estoimprovements in; the: method andapparatus described above. According: to the invention, the, tangential"velocityof the portion of. auxiliary liquid, flowing inwardly in the.channel system: referred to is changed byfriotionalforcesonly atvthewallsof the channels. There must, therefore, beno ribs 01* wingsprojecting into the. inwardly passing layers of the liquid andpreferably the channels should be entirely free from such parts.

In. order to free the particles eliectively from the main liquid and,obtain a sorting of the particles, there should be a. turbulency ofsuitable intensity in theflow of liquid through the channel system. Itshould be strong enough to keep the specifically lighter and the smallerparticles suspended in the inwardly directed current but must not bepowerful enough to prevent the heavier and the larger particles frommoving outward towards the openings in the bowl wall. This turbulentflow can be obtained by properly determining the amount of auxiliaryliquid passing inwardly in view of the dimensions of the channels;Considerable amounts of auxiliary liquid passing in the inward directionare generally required for this purpose, which increases thepowerconsumption and encunibers thesepa rating space, the latter effectbeing due to mixing ofthe main and the auxiliary liquids therein. Anincrease in the amount of auxiliary liquid increases the rate of flowthrough the separating space and thus impairs the result of theseparation.

According to the present invention, the desired d'egreeof turbulency isbrought about by using small amounts of auxiliary liquid flowinginwardly.

Turbulent flow is obtained only when the velocity of the liquid currentrelative to the piping or confining wallsof the current exceeds acertain critical value, one of the factors determining the latter'beingthe viscosity of the liquid. In the procedure previously referred to,the velocity of the inward current of liquid was higher than thecritical value. According to the invention, the liquid velocity requiredfor turbulent'flow is obtained by introducing the auxiliary liquid intothe system of channels with, or therein giving it, a rotational velocitysubstantially different from that of the bowl. It is evident that a highliquid velocity relative to the rotating channels can be achieved bycombining a low inward velocity with ahigh tangential velocitydifferential. v

For a better understanding of the invention, reference may be had to theaccompanying drawing, in which Fig. 1 is a vertical sectional view ofcentrifugal bowl made according to the invention, and

Fig. 2 is a similar view of. the outer part of a modified form of thebowl.

Referring to Fig. l, the main liquid is fed through a system oichannelsl into the chamber of the centrifugal bowl B, this chamber having aseparating zone divided into thin separating layers by the discs 2. Whenthe main liquid passes between the discs, the particles contained in themain liquid are separated more or less completely. They slide along thelower surfaces of the discs into, and are accumulated in, spaces has thesame rotational velocity as that of the bowl. In the channels 4a and 41)it is divided into one portion flowing outwardly and one flowinginwardly. It is now assumed as an embodiment of the invention that thechannels 4a and 4b contain no wings in the path of the inwardly directedflow of liquid, which may act as conveyors. When a liquid element movesinwardly, it assumes a tangential velocity relative to the bowl, becauseit is influenced only by forces which themselves are created by avelocity differential between the liquid and the system of channels. Thevelocity of an element moving within the channel 4a in the vicinity ofits lower boundary surface is changed by the frictional force betweenthe element and the surface.v This, in turn, is proportional to thevelocity of the liquid element relative to the surface. the inwardlyflowing liquid, the distance of which from the rotation axis issuccessively reduced, obtaining, at each'point of its path, a rotationalvelocity higher than the rotational velocity of its momentary point ofcontact with the boundary surface. When this velocity differentialreaches a suflicient value, turbulence appears. The above description isa considerable s mplification of the course of flow. It is complicatedby (among other things) a concentrated suspension of solid particlesmoving outward along the outer boundary surface of the channel. As thissuspension moves outwardly from within the bowl, it will, whenconveyed-only in the channel 4a by the friction at the boundary surfaceof the channel, rotate more slowly even when it is at a very smalldistance from the surface.

This results in 4 possible, however to make a general rule as to how theliquid is to be introduced into the channels in all circumstances. Themethod of introduction must be determined in view of theseparatingproperties of the particles tobe separated from one another.In some cases, it has proved advantageous to feed the auxiliary liquidinto the channel through a plurality of holes arranged in severalconcentric systems. With this manner of introduction, the ring 2| mayalso be supported by the bowl wall by means of ribs or lugs 8, withoutthereby impairing the action of the channels 411 and- 41). It is to benoted that the ribs 8 are placed outside the outermost series of holes5, since there is no inwardly directed flow of liquid in the channeloutside this series The invention also comprises modifications of theabove-mentioned procedure and the apparatus for putting it into effect.In the following, the modifications will be described in conjunctionwith a starch manufacturing process by which the starch is separatedfrom the gluten. The latter product has a flake-like consistency andlower specific gravity than the starch.

Starch and gluten separated from the main liquid between the discs 2enter the channels 411 and 4b as a concentrated suspension. In thesechannels, as previously described, it meets a turbulent inwardlydirected now of auxiliary liquid. With the proper degree of turbulency,the starch is separated and enriched in a layer which slides outwardlyalong the outer boundary surface of each channel 4a and 4b anddischarges through the ports 7 in the bowl periphery. The majority ofthe glutenous particles are kept suspended in the turbulent flow ofliquid, by which they are carried off in an inward direction towards thecenter of the bowl. One part of the gluten passes through the discinterspaces and leaves the separator bowl at the outlet [9, whileanother part is separated out, enters the channels 4a and 41) again, andis returned towards the center.

When a highly turbulent flow is required, the auxiliary liquid should befed into the annular chamber 6, to which the channels 4a and 41)converge at the bowl periphery. At the inner orifices of the channels 4aand 4b, the liquid will then have a higher tangential velocity inrelation to the bowl than if it is introduced between the inner andouter orifices of the channels.

tional velocity than that of the bowl. It is-imof holes.

It is important that the suspension be evenly distributedciroumferentially of the bowl even when it is only a small distance fromthe inlets to the channels. 4a and. 42). ,When wings are provided in thechambers 3a and 3b outside the discs, an uneven distribution results.With such members, the starch and the gluten would'be concentrated onthe front side of the members, reckoned in the direction of rotation.

In Fig. l, I have shown how the auxiliary liquid can be led through thechamber situated outside the discs 2 without wings or conveying membersbeing formed which may cause uneven sup ply of suspension along thecircumference of-the channels 4a and 4b. The space H communi cates withthe system for supply of auxiliary liquid through channels 9 in themember ID. The latter is disc-shaped or circular and has nopartsprojecting into the space outside the discs 2. It divides the outerportion of the separator bowl into upper and lower parts, whichcommunicate with one another only through the annular space 6. In thelatter, the heavy particles which have passed through the channels 4aand 4b accumulate. I-Ioles Illa, provided in the member In inside theouter edges of the discs 2, convey'the liquid which has passed throughthe discs in the lower part of the separator bowl into its upper part,which is provided with an outlet 19 for the discharge of the liquid.

Channels I may also be provided within member I ll for the supply of themain liquid from inlet pipe 20. ,f

Ribs may also be arranged on the outer boundary surfaces of the channels4a and 4b in order to force the layers slidingalong these surfaces tofollow the rotational speed of the channels. It is important that suchribs are not so deep as to allow a layer to be formed nearest to. theinner boundary surface of the channels 4a and 4b, where the auxiliaryliquid should flow without being conveyed by the ribs. 1

As shown in Fig. 2, the disc-shaped member is made up of two parts Naand I21). A'- rubber ring it, which establishes a tight joint betweenthese parts, is supported by a disc Id enclosed in the annular chamberIla. The auxiliary liquid is fed into the latter from the channels 9a,situated in a central annular member '65, through an annular chamber I6,which preferably is provided with radial conveyor ribs. ll fixed to theparts [20. and i211, and, if required, extending into the space Ila. Theauxiliary liquid should be prevented from flowing inwardly from chamberl6, and for this purpose I provide rubber tightenings or packings l8which make tight joints between the parts [2a and I22 and the centralinlet member l5. The latter; also in:

corporates channels for the main liquid, as in Fig. 1.

It will be noted that the channels ira-db have smooth inner walls (theWalls nearer the rotation axis) providing an unobstructed rotationsurface.

I claim:

1. In a centrifuge of the character described, a rotatable centrifugalbowl having a chamber including a separating zone, the bowl also havingan inlet communicating with said zone for supplying the material to beseparated thereto and an outlet in the peripheral wall of the bowl fordischarging separated solids from the bowl, a generally annular memberin the bowl rigidly connected thereto substantially concentric to saidperipheral wall and defining with said well a narrow annular channeldisposed outwardly from said zone and inclined to the rotation axis ofthe bowl and to the direction of the centrifugal force therein, thechannel affording communication between said zone and the peripheralpart or" the chamber at said outlet, means in the bowl forming anauxiliary liquid passage leading into said channel outward from itsjunction with said zone, and means for feeding an auxiliary liquid byway of said passage inwardly along the channel in countercurrent toseparated material from said zone, the channel having a smooth innerwall forming an unobstructed rotation surface at least along a majorpart of its inner portion adjacent said zone.

2. A centrifugal bowl according to claim 1, comprising also a generallyhorizontal disc shaped member in the bowl dividing the separating zoneinto upper and lower parts and having channels, said annular memberhaving holes forming a plurality or said passages, said annular memberalso having a hollow interior to which said disc channels lead, wherebysaid feeding means are operable to feed the auxiliary liquid inwardlyalong said first channel by Way of said disc channels, hollow interiorand Dassages.

3. A centrifugal bowl according to claim 1, comprising also a generallyhorizontal discshaped member in the bowl dividing the sep arating zoneinto upper and lower parts and having channels, said annular memberhaving holes forming a plurality of said passages, said annular memberalso having a hollow interior to which said disc channels lead, wherebysaid feeding means are operable to feed the auxiliary liquid inwardlyalong said first channel by way of said disc channels, hollow interiorand passages, said disc-shaped member also having a passagecommunicating with the bowl inlet for feeding to the separating zone thematerial to be separated.

4. A centrifugal bowl according to claim 1, comprising also a generallyhorizontal discshaped member in the bowl dividing the separating zoneinto upper and lower parts and having channels, said annular memberhaving holes forming a plurality of said passages, said annular memberalso having a hollow interior to which said disc channels lead, wherebysaid feeding means are operable to feed the auxiliary liquid inwardlyalong said first channel. by way of said disc channels, hollow interiorand passages, said annular member partly defining an annular chamberbetween the separating zone and said annular channel, said last chamberhaving smooth walls.

5. A centrifugal bowl according to claim 1, comprising also conveyorribs in the channel extending along the outer wall thereof.

6. A centrifugal bowl according to claim 1, in which said passage andfeeding means include a system of channels terminating in said annularchannel.

7. A centrifugal bowl according to claim 1, in which said feeding meansincludes a chamber within the bowl chamber and located between saidchannel and said peripheral outlet.

8. In a centrifuge of the character described, a rotatable centrifugalbowl having a chamber including a separating zone, the bowl also havinsan inlet communicating with said zone for supplying the material to beseparated thereto and a peripheral outlet for discharging separatedsolids from the bowl, generally horizontal discshaped member in the bowldividing the separating zone into upper and lower parts and having afeed passage communicating with said inlet to deliver to the separatingZone the material to be separated, said member also having an auxiliaryliquid channel, and a hollow ring at the periphery of the disc-shapedmember and having a distributing chamber fori'eceiving auxiliary liquidfrom said channel, the ring defining with the bowl a narrow annularchannel disposed outwardly from said zone in inclined relation to therotation axis of the bowl and affording communication between said zoneand the peripheral part of the bowl, the ring having openings leadinginto said annular channel for feeding auxiliary liquid inwardlytherealong.

9. A centrifugal bowl according to claim 8, in which the ring defineswith the bowl a second narrow annular inclined channel affordingadditional communication between said zone and the peripheral part ofthe bowl, the ring also defining with the bowl periphery an outerannular chamber adjacent said peripheral outlet and to which saidannular channels converge.

10. A centrifugal bowl according to claim 9, in

which the ring has openings leading directly from the distributingchamber to said outer annular chamber.

11. A centrifugal bowl according to claim 8, in which said member has ahole located in the separating zone and through which said upper andlower parts communicate.

JOHN A. ASPEGREN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 495,681 Peck Apr. 18, 1893 560,630 Peck May 19, 1896 1,154,575McCallum Sept. 21, 1.915 2,488,747 Strezynski Nov. 22, rate

